In the production of aluminum through electrolysis of aluminum oxide dissolved in a molten bed of cryolite or other electrolyte, the interior of an electrolytic cell is lined with prebaked carbon blocks joined together to form a unitary carbon cathode structure for the cell. The union of the carbon blocks has, in the past, generally been achieved through the use of a hot ramming mix formed from a carbonaceous aggregate such as calcined anthracite and a binder such as a high melting point pitch. This hot mixture was rammed into the spaces between adjacent blocks placed in the bottom of the cell. After compaction of the ramming mix into these spaces the assembly of blocks and joints was baked at a sufficiently high temperature to carbonize the binder, and in that manner join the individual carbon blocks together to form the unitary cathode structure. In this manner the carbon blocks not only served as a cathode but also formed an open topped container, being both the sides and bottom liner of the cell for holding the molten salt bath. As a container for the electrolyte, the absence of cracks and leaks in the carbon block liner becomes highly desirable, particularly in view of the great expense and down time associated with tearing down a cell for repair and/or reconstruction.
Recent environmental concern has been expressed over the use of the hot pitch in the fabrication of a cell with the hot ramming mix and its resultant hot toxic vapors, making desirable a binder which is nontoxic to workers during construction of a cell, while retaining the capability of keeping the cathode structure intact as a liner, with no leaks or cracks. Various cold ramming mixes consisting of aggregate, pitch and solvent for the pitch have proven ineffective in binding to the walls of the carbon blocks. The lack of an effective bond between the carbon blocks and the ramming mix allows the bath liquid to eventually penetrate between the carbon blocks to the cell, bottom, thereby requiring frequent repairs and replacement, representing long periods during which the cell is inoperative (down time) thereby creating significant maintenance and operating burdens in the production of aluminum.